This invention relates to an improved transmission. It may be considered an improvement on the hydromechanical transmission described in U.S. Pat. No. 4,168,637 which issued Sept. 25, 1979.
The transmission of U.S. Pat. No. 4,168,637 and the transmission of the present invention each provides a hydromechanical infinitely variable transmission. Each provides for improved utilization of vehicle engine power by enabling the engine to operate within a narrow speed range which has been optimized for minimum emissions, maximum fuel economy and maximum power, regardless of vehicle operating conditions. There are many identical features.
In U.S. Pat. No. 4,168,637 there were two sets of planetary assemblies, each one of which had at least one sun gear, ring gear, carrier, and planet gears. In the present invention these two sets of planetary assemblies are replaced by a single Ravigneau-type planetary assembly.
The present invention possesses all of the advantages of our U.S. Pat. No. 4,168,637 and also possesses the further advantages of simplicity, lower manufacturing cost, reduced size, and reduced weight. These advantages are a result of the current invention having just one ring gear, just one planet carrier, and simplified clutch oil feeds.
Another very important cost advantage accrues to the form of the invention which has a particular gearing ratio. For the particular gearing ratio which produces equal hydraulic horsepower on each side of the shift, the ring-to-sun ratio is 3:1 for both sun gears. This means that the two sun gears as well as the first planet gear are the same diameter and have the same number of teeth. Furthermore the second planet gear may also have that same diameter and have the same number of teeth. If these are spur gears (not helical), then all of the gears in the transmission are identical except, of course, for the ring gear. If the gears are helical (which is standard practice for passenger cars) then the first planet and second sun are identical. And, also, the first sun and the second planet may be identical. The tooling cost advantage from all of this is readily apparent.
In addition, all of the advantages of low hydraulic horsepower and high efficiency of U.S. Pat. No. 4,168,637 are also present, as is the start up in forward and reverse.